It has been found that under certain circumstances and for persons with a particular but not unusual type of hearing defect, that a hearing aid providing good, directional response is very desirable. People whose hearing handicap is that they are deaf in one ear but have at least some minimal level of hearing in the other ear find it very difficult to tune into and understand a particular speaker or sound source in the presence of other background noise sources. Persons with such a single ear hearing loss are able to hear with their good ear, but are unable to differentiate and separate the sounds from various sources. In other words, they are able to hear but not to understand. This phenomenon is known as the "cocktail party" effect it makes it extremely difficult for a mono-aurally handicapped person to participate effectively in a situation with multiple sound sources such as at a group discussion or at a cocktail party.
Among the devices proposed in the prior art, and currently commercially available, one which has achieved some popularity and is known as the cross-aid device. This device consists basically of a subminiature microphone located on the user's deaf side, with the amplified sound piped into the good ear. While this compensates for deafness on one side, it is not very effective in reducing the cocktail party problem. Other efforts in the prior art have been largely directed to the use of moving, rotatable conduits which can be turned in the direction which the listener wishes to emphasize (see for example U.S. Pat. No. 3,983,336). Alternatively, efforts have also been made in using movable plates and grills to change the acoustic resistance and thus the directive effect of a directional hearing aid (see U.S. Pat. No. 3,876,843 Moen). None of these efforts have proved to be satisfactory. Old-fashioned ear trumpets has been effective in providing amplification and directionality, but they went out of favor with the advent of electronic hearing aids.